While a proposed random access method as set forth below is applicable to various types of wireless communication, the random access method will be described below in the context of a WLAN system as an example of a system to which the present invention is applicable.
Standards for a WLAN technology have been developed as Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards. IEEE 802.11a and 802.11b use an unlicensed band at 2.4 GHz or 5 GHz. IEEE 802.11b provides a transmission rate of 11 Mbps, and IEEE 802.11a provides a transmission rate of 54 Mbps. IEEE 802.11g provides a transmission rate of 54 Mbps by applying Orthogonal Frequency Division Multiplexing (OFDM) at 2.4 GHz. IEEE 802.11n provides a transmission rate of 300 Mbps for four spatial streams by applying Multiple Input Multiple Output-OFDM (MIMO-OFDM). IEEE 802.11n supports a channel bandwidth of up to 40 MHz and, in this case, provides a transmission rate of 600 Mbps.
The above-described WLAN standards have evolved into IEEE 802.11ac that supports a transmission rate of up to 1 Gbit/s by using a bandwidth of up to 160 MHz and supporting eight spatial streams, and IEEE 802.11ax standardization is under discussion.